In particular, the invention relates to a method for both dry and underwater installation of a waterproof liner that is suitable for preventing both ground erosion and leaks of water caused by seepage through the bottom and/or side banks, in hydraulic canals, irrigation canals or in basins for collecting water.
As is known, the bottom and the side banks of canals for conveying water, or of collecting basins, often have to be protected by a suitable waterproof liner, to prevent both ground erosion, and loss of water through seepage through the bottom and the side banks.
In the past the bottom and the sides of a canal were lined by laying a plurality of concrete slabs next to one another and subsequently sealing the joints between slabs with cement or joining elements for example waterstop.
Nevertheless, the concrete slabs had to be laid dry, in the absence of water in the canal; in case for example of hydraulic canals intended to serve several installations or intended for irrigation, the need to operate dry involved interrupting the flow of water and the services for which the canals were intended.
Further, the concrete slabs are subject to cracking and splitting, and sometimes have a high degree of permeability with consequent losses of water through seepage through the concrete and the splits or defective joints thereof. Using concrete slabs also entails onerous conveying and installation operations, depending on the conformation of the ground, with high costs and excessively long laying times; experience has thus shown that the use of concrete slabs entails numerous problems.
In an attempt to improve the degree of waterproof, in addition to simplifying the operations of laying the waterproof liner, the use of glass fibre panels or of panels of another material has been proposed that are covered with a resin, and are fixed by anchoring, as disclosed for example in U.S. Pat. Nos. 3,854,292, 5,806,252 and US 2002/0094238. Nevertheless, also these solutions entail the need to lay the waterproof liner only dry and to perform maintenance operations; with a consequent interruption to the flow of water.
In the past, the use of waterproof panels comprising a layer of clay was also proposed, for example a bentonite mixture in powder or granules, in which the layer of clay is confined between two textile containing layers, for example a geotextile, which are necessary to enable the bentonite to be wetted, and in which the layers of textile are joined by tie rods or intermediate connecting members configured for maintaining the two layers of textile at a suitable distance during swelling of the bentonite caused by wetting. In fact, during the wetting process, the particles of clay tend to expand, gradually reducing the passage and seepage of water into the underlying ground. Nevertheless, the use of waterproof panels comprising a layer of bentonite, confined between two layers of textile, does not permit the quality and thickness of the entire panel to be controlled; it also has a relatively high permeability coefficient, unless complex and costly formulations are resorted to, and also entails the release of polluting substances contained in the bentonite mixture, through the layers of containing textile, which are not watertight.
It is also known that the behaviour of the bentonite depends on the mineral components and on the chemical and physical properties thereof; accordingly, the degree of permeability of the bentonite is difficult to control because it is subject to variations with temperature and of the bentonite mixture.
Using the waterproof panels in bentonite thus makes it difficult to maintain the degree of permeability at a low, substantially constant and controlled value; it also always requires the waterproof liner to be laid and formed in the absence of water in the canal or basin.
Waterproof bentonite panels are disclosed, for example, in EP 0491454, EP 1141490, DE 4221329 and DE 4405523.
In particular, EP 0491454 relates to a waterproof panel comprising an intermediate bentonite granular layer, confined between two layers of textile that are structurally interconnected by means of filaments by perforating the bentonite layer to interconnect the fibres of the two layers of textile over the entire surface of the panel.
EP1141490 in turn relates to a waterproof mat, which again comprises a lower support layer and an upper cover layer of fabric or film of plastics, with connecting elements that traverse an intermediate bentonite layer, in which the lower support layer is provided with an adhesive, which is insoluble in water, covered with grains of sand that are suitable for providing great static friction with the ground.
DE 4221329 also relates to a waterproof mat comprising a bentonite layer confined between two containing layers joined by parallel seams suitable for forming tubular cells, in which the upper layer is provided with slits that are suitable for enabling the bentonite to exit partially.
Lastly, DE 4405523 also relates to a waterproof mat consisting of a double fabric filled with sand, bentonite or concrete, in which the side edges of the mat are configured so as to permit simple superimposing of the edges of two adjoining mats.
Using bentonite panels or mats is inadvisable not only because bentonite does not permit suitable control of the degree of permeability of the panel or mat, in addition to the need to work in the absence of water in the canal or basin, but the porous nature of the two layers confining the bentonite, or the presence of slits entails possible pollution of the water that flows along the canal or that is contained in the collecting basin; further, in addition to the need to install the liner on the bottom and/or the banks of the canal or basin only dry, in the absence of water, the use of bentonite or cementitious mixtures envisaged for performing the dual function of waterproof and ballasting the waterproof liner does not permit appropriate and homogeneous waterproof, being also critical in the case of splitting of the bentonite or concrete layer, in particular, between joints of adjoining panels.
It has also been proposed to construct a liner, both in the presence of running water and waves, for the sole purpose of reducing the phenomenon of ground erosion. Examples of liners installed directly underwater are found in GB 1111453, U.S. Pat. No. 3,538,711, WO 8101719 and U.S. Pat. No. 5,720,576.
In particular, GB 1111453 illustrates a method for constructing a protective liner underwater, substantially consisting of individual panels comprising two superimposed layers of flexible material, between which a cementitious, asphalt or other material that is suitable for forming a ballast is injected; the panel is further configured with a plurality of interconnecting areas between containing layers of the ballast material, in which openings are formed at the joining points, so as to prevent the panel moving away or breaking because of the sucking action of the flow of water or of the hydrostatic pressure of the water in the ground. Again, a protective panel is proposed for the sole purpose of preventing or limiting the erosion of the underlying ground, which is completely unsuitable for providing waterproof.
U.S. Pat. No. 3,538,711 in turn proposes using ballasted panels for controlling and preventing coastal erosion which substantially consist of a long flexible tubular element, formed of plastic sheets welded along the edges, or of fabric that is filled with sand or small stones; tubular elements are simply positioned side by side, or superimposed, to protect a preset area.
WO 8101719 discloses in turn the use of long tubular elements made of plastics that are filled with concrete during laying underwater, the elements being laid on the bottom with the help of a diver. Also this solution, like the preceding solutions, does not permit total waterproof of areas of large dimensions, being again critical in the event of cracks or splitting of the tubular element at joining points; it further makes it impossible to replace and/or repair the tubular elements underwater.
In U.S. Pat. No. 5,720,576, lastly, it has been proposed to use waterproof membranes made of polymer or geosynthetic material, more commonly known as “geomembranes” to waterproof dams or hydraulic structures in which the membranes are sealingly connected, by superimposing and clamping the edges by means of metal sections anchored to the hydraulic structure; such a solution, in addition to being extremely complex and costly, requires a comparatively long laying time, being completely unsuitable for laying underwater waterproof liners in canals or in the presence of running water.
WO2012040269 discloses a method and a device for draining off water seeped in a soil underlying a hydraulic structure, such as a canal, basin, dams and the like. A liner, consisting of a geomembrane constituted by a plurality of waterproof sheets, is laid on the bottom wall and side walls of the hydraulic structure, by providing the liner with one-way gravity drainage valves which extend longitudinally with respect to the lateral walls or the bottom wall of the hydraulic structure. The edges of adjacent panels are superimposed and may be welded together to form said valves; therefore it is not sure that, in the presence of negative pressures, water contained in the hydraulic structure is unable to seep under the waterproof liner, in the regions where the edges of adjacent panels are superimposed. The waterproof liner is anchored to the bottom and to the walls of the channel by placing concrete slabs over the covering.
In general, the prior art has thus provided to protect canals or waterways from the corrosion of the ground and/or of the side banks, i.e. to form a waterproof liner by layers of bentonite material confined between layers that are permeable to water to enable the bentonite to expand in a controllable manner only partially. It has also been proposed to protect the bottom and the banks of canals by panels placed underwater, formed at the moment of placing thereof, by means of complex apparatuses.
Previously proposed methods and systems for laying liners in addition to requiring comparatively long and costly procedures, in particular, in the case of bentonite panels, do not permit constant control of the degree of permeability. None of the preceding cases thus permits a complete adequate seal of the entire waterproof liner, in particular, in the zones joining adjoining panels, or the possibility of intervening subsequently for performing repair and maintenance works underwater, or repairing and/or replacing individual damaged panels by operating always in the presence of water to restore the entire seal of the waterproof liner; further, it is not possible to connect to existing structures so as to ensure the impermeability thereof.
There accordingly exists the need to find a new solution for installing and laying underwater, in canals and basins, a waterproof liner comprising a plurality of panels that are alongside one another, that enables the various panels to be sealingly connected directly during laying underwater, so as to reduce significantly the time and cost of laying the entire liner, also permitting close control of the quality of the work and a high degree of waterproof.